What it is
Feline leukemia virus spreads between cats through saliva and close contact: grooming, shared bowls, bites. It suppresses the immune system and causes cancers and anemia; infected cats have shortened lives. Cats are usually tested for it before vaccination.
Kittens
Guidelines recommend the vaccine for all kittens: two doses three to four weeks apart from around 8 weeks old, and a booster a year later. Kittens are the most susceptible and their future lifestyle is unknown.
Adult cats
After the first year, boosters continue for cats at risk: those that go outdoors, live with an FeLV-positive cat, or are in multi-cat households with unknown status. Low-risk indoor cats may stop or move to a longer interval on the vet’s advice.
Catteries
Some ask for FeLV, particularly for cats that go outdoors; others ask for a negative test instead. It is worth keeping both the vaccination and the test result in your cat’s record.
Sources
Rules and guidelines change, and businesses set their own policies. Confirm with your vet and with whoever is asking.